In the past, an electronic device socket inserted between such an electronic device and a circuit board so as to detachably attach to the circuit board an integrated circuit package or other electronic device having a large number of terminals such as a land grid array (hereinafter referred to as an “LGA”) or a ball grid array (hereinafter referred to as a “BGA”) has been in wide use. Such an electronic device socket is provided with a plurality of contact terminals for electrically connecting the terminals of an electronic device and contacts of the circuit board. Further, in an electronic device socket, to transmit signals output from the electronic device with a high reliability to the circuit board, various configurations are provided for preventing poor conduction of the contact terminals and suppress the generation of noise (see JP Registered Utility Model No. 3099091 and WO99/41812.
For example, the Abstract of JP Registered Utility Model No. 3099091 discloses “a semiconductor package socket having an insulating board 1 forming a plate shape for carrying a BGA 21, through holes 2 passing through this board in a thickness direction, and conductive coil springs 41 contacting the inner surfaces of the through holes 2 and able to expand and contract in an axial line o-direction of the through holes 2, the coil springs 41 and solder balls 22 being electrically connected, wherein the inner surfaces of the through holes 2 are provided with metal platings 3 to enable high frequency current to flow in the axial line o-direction.”
Further, the Abstract of WO99/41812 discloses “a multilayer printed circuit board 20 having at least four conductor layers comprised of ground conductor layers 23 and 25 and power conductor layers 22 and 24 alternately stacked, provided with a plurality of through hole conductors 21a, 21a′, 21b, and 21c and attaching probe contacts 3a, 3b, and 3c electrically connected to terminals of a DUT 4 to the remaining through hole conductors 21, 21b, and 21c excluding at least one through hole conductor 21a′. Said ground conductor layers are electrically connected to the through hole conductors 21a and 21a′, said power conductor layers are electrically connected to through hole conductors 21b, and capacitors CA and CB using the material of the printed circuit board 20 as dielectrics are formed between the ground conductor layers and the power conductor layers.”
However, the operating frequencies of electronic devices have been rising in recent years. Further, along with the rise in the operating frequencies, the frequencies of the signals propagated between the electronic devices and circuit boards have also been rising. The frequencies of the signals have become 1 GHz or more in some cases. Therefore, to enable transmission of such high frequency signals with a high reliability, further improvement of the conductivity of the electronic device socket is sought.